As part of a broader interest in immune complex-mediated inflammation and vascular injury, this proposal focuses on the potential of human platelets and endothelial cells to participate actively in such processes. Specifically targeted for study are platelet and endothelial cell Fc(IgG) receptors including factors governing their expression, function and effective interaction with IgG-containing immune complexes. Previously noted stable difference among normal donors in quantitative expression of platelet FcgammaRII will be subjected to genetic analysis by family and twin studies and RFLP analysis. A systematic examination of the properties of an IgG complex that favor FcR-mediated platelet activation, and the inhibitory effects of plasma, will be undertaken. In addition, electron microscopic localization of platelet FcgammaRII and assessment of the effect of FcgammaRII crosslinking on F-actin formation are planned. Human umbilical vein endothelial cells will be systematically analyzed for Fc(IgG) receptors and the membrane glycoproteins serving this function characterized. Finally, immunologically mediated platelet-endothelial cell interactions will be explored.